1. Field of the Invention
The present invention relates to an ultrasonic motor that utilizes oscillation of an oscillator of, e.g., a piezoelectric element, and more particularly to an ultrasonic motor that utilizes elliptic oscillation produced when longitudinal oscillation and torsional oscillation are simultaneously excited.
2. Description of the Related Art
In recent years, as a new motor that substitutes for an electromagnetic motor, an ultrasonic motor that utilizes oscillation of an oscillator of, e.g., a piezoelectric element attracts attention. As compared with a conventional electromagnetic motor, this ultrasonic motor has advantages in that, e.g., low-speed and high thrust can be obtained without a gear, retaining force is high, resolution is high, quietness is high, and magnetic noise can be prevented from being generated.
Specifically, for example, when an oscillator formed of an ultrasonic oscillator is pressed against a rotor that is a driven member trough a frictional member fixed on the oscillator, frictional force is generated between the frictional member and the rotor, and the rotor is driven by using this frictional force.
In more detail, when longitudinal oscillation and torsional oscillation are simultaneously generated in the ultrasonic oscillator, elliptic oscillation as a combination of these oscillations is produced at an end face of the ultrasonic oscillator, and the rotor is rotated by utilizing this elliptic oscillation. As a technology concerning such an ultrasonic motor, for example, JP-A 9-85172 (KOKAI) discloses the following technology.
That is, JP-A 9-85172 (KOKAI) discloses an ultrasonic motor comprising: a rod-like elastic body; a plurality of holding elastic bodies provided on a side surface of the rod-like elastic body to be integral with the rod-like elastic body; a plurality of pairs of laminated piezoelectric elements arranged in such a manner that each piezoelectric element is held at both ends by each of the plurality of holding elastic bodies and forms an acute angle between a displacement direction thereof and a longitudinal direction of the rod-like elastic body and that the plurality of pairs of these piezoelectric elements are inclined in opposite directions; a plurality of oscillation detecting piezoelectric elements provided between the laminated piezoelectric elements and the holding elastic bodies; a friction block provided on an end face of the rod-like elastic body; a rotor arranged being appressed against the friction block by pressing means; and power supplying means for applying alternating voltages having predetermined frequencies and intensities associated with phases or amplitudes of signals output from the oscillation detection piezoelectric elements and having phase differences to the respective pairs of laminated piezoelectric elements. In this ultrasonic motor, longitudinal oscillation and torsional oscillation are simultaneously excited in the rod-like elastic body, whereby ultrasonic elliptic oscillation is excited on the friction block, thus driving the rotor to rotate.
Specifically, according to the technology disclosed in JP-A 9-85172 (KOKAI), one or more pairs of laminated piezoelectric elements are held between the holding elastic bodies each having a concave portion into which the laminated piezoelectric element can be inserted and the rod-like elastic body. Further, the holding elastic bodies are arranged to abut on the laminated piezoelectric elements, compression stress is applied, and the laminated piezoelectric elements are fixed to the rod-like elastic body through screws in this state.
Therefore, when adopting the configuration disclosed in JP-A 9-85172 (KOKAI), each holding elastic body used for fixing the piezoelectric element is an essential constituent element, and concave portions in which the holding elastic body and the piezoelectric element are arranged must be formed in the rod-like elastic body. As described above, it is difficult to simplify and miniaturize the structure of the oscillator by the technology disclosed in JP-A 9-85172 (KOKAI).
Further, since a configuration that a plurality of oscillation detecting piezoelectric elements are provided between the plurality of pairs of laminated piezoelectric elements and a holding elastic body is adopted, required wiring lines are two wiring lines for driving and two wiring lines for oscillation detection per phase. That is, when adopting two-phase driving, as many as the eight wiring lines are required, which is a factor that obstructs the miniaturization.